1. Field of the Invention
The present invention relates to a packet communication system for dividing data into digitalized blocks for transfer, and in particular to an inter-network connecting system between a main network with an exchange function and a subnetwork without an exchange function.
For example, there is a public network as the main network, and there is, a customer station network as the subnetwork, connected to the public network.
2. Description of the Related Art
Conventionally, data communication networks have been developed based on a telephone exchange network, however, accompanied by the rapid expansion of the data processing field, various problems due to lack of functions in the communication systems have been pointed out. As a countermeasure to solve these problems, an integrated services digital network (ISDN) has been provided. The ISDN is being reconstructed from a conventional narrow band ISDN (64 Kbps) to a broad band ISDN (150 Gbps) in which various services such as a data communication network, facsimile network, voice network, various private line networks, picture communication network, and so forth are integrated into one digital communication network. Due to the rapid development of communication techniques such as the above-mentioned ISDN, data processing techniques and so forth, it has been desired to provide a data communication system in which various terminals and data instruments are combined, and in which data and resources can be efficiently utilized. In particular, to correspond to the demands for broad band and multimedia services, for a variety of communication configurations, etc., it has been desired to develop an economic, easy to expand, and efficient system in a subnetwork as well as the main network, when the subnetwork (such as a customer station network) is connected to the main network (such as a public network).
In a conventional subnetwork, a network connecting system is known which comprises a PBX having an exchange function and a call processing processor for controlling the PBX so it can be connected to a main network. In this conventional system, however, as described later in more detail with reference to the drawings a call process setting means is necessary in the subnetwork. Thus, if the subnetwork is used as a customer station network, it is suitable for a big company, but there is a problem in economy for small companies or a standard home.
In another conventional network connecting system, there is a system in which the exchange function necessary for the subnetwork (for example a customer station network) is provided in an exchange of a main network. In this conventional system, since the subnetwork itself does not have the exchange function, the cost can be made lower than the above-mentioned first conventional system.
In this conventional system, however, as described later in more detail with reference to the drawings, even for data transfer between terminals in the subnetwork, a physical communication path is provided in a subscriber line between the subnetwork and the main network for folding the signal in the exchange in the main network so that there is a problem in that the traffic amount in the exchange is increased and the capacity of the exchange must be large.
Also, in order to effectively accommodate a plurality of subscribers, when a subscriber network constitution is utilized in which a multiplexing line concentration unit is inserted between the subscriber lines, it is necessary to make the capacity of the feeder loop large and to provide an exchange function (remote exchange function) for suitable distribution of data from the feeder loop to respective subscribers.